Fiber Characteristics for Next-Generation Ultra-Long-Haul Transmission Systems

The availability of coherent detection and its capability to compensate for chromatic dispersion will have a clear impact on system design and fiber characteristic especially for ultra-longhaul systems. Introduction The revolution brought by coherent detection associated with digital signal processing and multi-level modulation format started around 5 years ago with a first demonstration of the concept [1], then a demonstration of large chromatic dispersion compensation at 40Gb/s [2], a WDM Ultra Long Haul experiment [3] and a first 100Gb/s experiment [4]. For 2 years, almost all record experiments reported have used coherent detection and most of them do not use optical dispersion compensation in the line. Fig 1 depicts the evolution of the record experiments by plotting the product of capacity times distance versus the years as a function of detection scheme used. (corresponding nearly at the wavelength where the signal was transmitted) in order to minimize the chromatic dispersion accumulation at the end of the link. Fiber attenuation was around 0.205dB/km and the effective area was relatively small, around 55µm². Nevertheless, EDFAs opened the road not only to ultra long haul unregenerated links but also to WDM transmission. Soon after their introduction in laboratory experiments, it has been observed that DSF was not adapted to multi-channel transmissions. Non linear effects, especially Four Wave Mixing, generate large signals degradations prevent transmissions over long distances.